Method for regenerating catalyst by combustion



- `Au@ 14, 1956 J. GUTHRIE 2351x979 1 METHOD FOR REGENERATING CATALYSTBY COMBUSTION Filed March 28,' 1952 2 sheets-sheet 1 WATE Tumbma J.GuTHRn-z 2,758,979

METHOD FOR REGENERATING CATALYST BY COMBUSTION Aug. 14, 1956 @e335 EJE;Clbbor'rze United States Patent METHOD FOR REGENERA'I'JNG CATALYST BYCONIBUSTION `lames Guthrie, Sarnia, Ontario, Canada, assigner to EssoResearch and Engineering Company, a corporation of Delaware ApplicationMarch 23, 1952, Serial No. 279,061

1 Claim. (Cl. 252-417) This invention relates to catalytic processes andrelates particularly to the use of gas turbines for supplying air or thelike to a catalyst regenerator. Most specifically, it relates to aprocess and apparatus wherein a gas turbine is so integrated in apetroleum cracking system that the turbine exhaust gas is used as theair required for combustion of the carbonaceous catalyst deposit in aiiuid catalyst regenerator.

ln recent years catalytic cracking processes have gained prominence inthe conversion of crude petroleum, and fluid catalytic cracking hasassumed a particularly important position in the petroleum industry. lnall catalytic cracking processes, whether in a fixed bed, a moving bed,or turbulent uidized bed, hydrocarbon vapors are contacted with catalystat suitable temperatures whereby heavy molecules are cracked to yieldmore valuable lighter products, especially gasoline. However, duringsuch cracking the catalyst gradually becomes covered by a carbonaceousdeposit which reduces the catalytic activity of the catalyst. As aresult, after a certain residence time in the cracking zone the catalystmust be regenerated by combustion of the carbonaceous deposit.

Such regeneration represents one of the major steps in modern catalyticcracking processes and especially in uid operations usually requires alarger vessel than the principal cracking reaction. The cost of therequired air compressors, usually driven by electric motors or by steamturbines, as well as the necessary boilers or electrical power system,constitute one of the iarge cost items in the operation of suchcatalytic cracking systems. Consequently the regeneration stage oftenlimits the overall cracking capacity of a given commercial unit.Furthermore, conventional units usually require auxiliary burners whichare used for heating the air whenever the regeneration step is tirststarted.

Heretofore some improvement in economy has been obtained by using thehet exhaust gas from catalyst regenerators to drive a dow-type gasturbine. However, this modication did not in any way affect the majorinvestment required for compressors and incidental prime movers neededto feed air into the regenerator initially, nor did it eliminate theneed for auxiliary burners required in starting up the operation of aconventional catalyst regenerator.

Accordingly, it is an object of this invention to improve the operationol catalytic cracking processes, and particularly to reduce capitalexpenditure. Another object is to provide a cracking plant which can beoperated without requiring the conventional air compressors and primemovers needed to drive such compressors. Still other objects as well asthe nature of the present invention will become apparent from thesubsequent description as well as the attached drawing wherein:

Fig. l is a diagrammatic illustration of a system comprising acombustion gas turbine which can be used according to this invention forsupplying the air requirements of a catalyst regenerator;

Fig. 2 is a diagrammatic illustration of a similar but more elaboratesystem containing a heat exchanger for extracting heat from theregenerator combustion gases as well as an electric power generator, asa result of which a uid catalytic cracking unit may be made still moreeconomical both with respect to air requirements and power forauxiliaries.

ln the subsequent description it will be understood that, unlessotherwise stated, whenever the expressions gas turbine or turbine areused, a gas turbine of the combustion type rather than of the ow orsteam type is meant. In the latter case, for instance, steam must firstbe brought up to the desired pressure and temperature in an auxiliarypower plant before it is fed to and expanded through the turbine Wherepower is generated. In contrast, in a gas turbine air is usuallycompressed by an axial dow compressor, fuel is injected into thecompressed air and burned in a combustion chamber, the hot combustiongases are expanded through the turbine proper, and discharged to theatmosphere. Where air is expensive because of required purification, aso-called closed cycle may be used wherein the exhausted air may be usedover again.

The gas turbine itself drives its own compressor and any excess powermay be used to drive a useful load. While the combustion gas turbinerequires some external means such as an electric motor to start it andget it up to partial speed, it is otherwise a completely self-containedpower plant. lt is .not necessary to make any steam or condense it.

Thermal eciency of a gas turbine to its output shaft may range fromabout l5 or 17 percent upward, depending on permissible maximumtemperature and on various modifications of its operation. For instance,when some ot' the heat of the exhaust gases is utilized for pre-heatingthe compressed air, the thermal etciency may be raised to some 20 to 30percent. Thermal el'liciency may also be increased by compressing theair in two stages, with water cooling between stages. This arrangementmakes the second-stage compressor smaller and more eicient, more thancompensating for the heat lost.

For flexibility and economy, the turbine may be a twoshaft ormultipleshaft unit, rather than a singie-shaft unit. For instance, in atwo-shaft unit the turbine may be split into a high-pressure and alow-pressure turbine unit in such a fashion that the exhaust from thehigh-pressure unit drives the low-pressure um't. ln such a case thehigh-pressure turbine may be used entirely to drive the compressor andthe mechanically independent low-pressure turbine may be connected tothe output shaft; or when a two-Stage compressor and intercooler areused, the high-pressure turbine may drive both the high-pressurecompressor and the output shaft, while the low-pressure turbine maydrive the low-pressure compressor. The main advantage of the multi-shaftturbine is its ability to have its compressor speed adjusted to give theneeded air iiow, independently of the output speed.

Still other modifications and variations in the mechanical arrangementand operation of the gas turbine, as such, are well known in the art.They have been summarized above only incidentally to the description ofthe present invention, the essence of which lies in the combination ofthe gas turbine with a catalyst regenerator in such a fashion that theturbine exhaust serves to supply air to the catalyst regeneration zoneas described hereafter.

Referring specically to Figure l of the drawing, atmospheric air orother combustion supporting gas from line l may enter axial iiowcompressor 2 where it is compressed to about 60 to 200 p. s. i. gauge,or preferably to 150 p. s. i. gauge, or any other pressure required forthe particular power output and desired conditions of the turbineexhaust gases. The compressed air. may pass. via line.. 3. through heatlexchangerY 4 where it may be heated to about 300 to 600 F. by the hotturbine exhaust gases passing through line S. The hot compressed lair isthenV passedy to turbine` combustion chamber vwhere it is mixed with afuel such as diesel oil, burner fuel, hydrocarbon -gas or powdered coalinjected through line 7. According to common practice the air is used inat least about 3 to 6 times the theoretical amount required to burn thefuel inthe combustion chamber. The hot excess air and combustionproducts pass from combustor 6 through line S to turbine 9 at atemperature of about 800 to 2000 F., preferably 1200 to 1500 F.,depending on the inherent limitations of themetal used in the turbine.On expansion through turbine 9 enough power is produced to drive bothair compressor 2 by means of shaft 10 and electrical generator 11l orany other load attached to output shaft 12. In normal operation theturbine may be operated at a temperature to just operate the compressor2 and have no net power output or conversely, only a fraction of thetotal power produced in turbine 9 may be used for driving the compressor2, the balance of power 4generated being available to drive any otherload. Shaft speeds may be of the order of about 4000 to 10,000 or morerevolutions per minute.

The expanded oxygen-rich exhaust gases pass from turbine 9 through line5 at a temperature of about 400 to 900 F. and preferably at onlyslightly superatmospheric pressure, e. g. l to 25 p. s. i. gauge, as maybe 'required for catalyst regeneration. Finally the gas may be cooled toabout 400 to 600 F. in heat exchanger 4 to obtain optimum conditions oftemperature and pressure for feeding to a conventional catalystregenerator 17 wherein itv serves to oxidize carbonaceous deposits offspent catalyst particles. For instance, spent catalyst particles may bewithdrawn from a conventional fluid catalytic cracking reactor 26 viastandpipe 27 and mixed into the turbine exhaust gases passing throughline 15. The resulting mixture of catalyst particles and air then maypass in the form of a suspension through riser 16 into regenerator 17,where carbonaceous deposits are burned off the catalyst at temperaturesbetween about 850 and 1200o F. Because of the relatively large diameterof vessel 17, the mixture of catalyst and gas forms a dense turbulentliquid simulating bed of solids in the lower part of vessel 17 with amore dilute phase thereabove, as is well known per se. 'Regeneratedcatalyst particles may be withdrawn from vessel 17 via standpipe 18 andreturned to reactor 26 together with fresh cracking feed such as gas oilor the like. Hot ue gas may be withdrawn overhead, preferably afterpassage through a cyclonic dust separator 19, and passed via line 20 toa.

waste heat boiler 21 for recovering additional heat.

From the foregoing it will be seen that a plant designed as describedabove avoids any need for separate air compressors to supply air to thecatalyst regenerator, since the oxygen-rich exhaust from the turbine iswell suited forV use in the regenerator.

Furthermore, a plant designed according to the present invention has theadvantage of eliminating any need for an auxiliary burner such as isotherwise required in' conventional catalytic cracking units.Specifically, when a fluid catalytic cracking plantis first started, itis essen-V tial that the air fed to the regenerator be heated to about650 to 700 F. before any oil can be added to the reactor. This heatduring start-up has been heretofore obtained through they use ofauxiliary burners which have represented a substantial portion of thetotall investment required, although the actual need for such burners islimitedito a very small percentage of the operatingv lifel of theprincipal vr:cracking unit. The present invention avoids the' need forany suchauxiliary burners since the turbine exhaust gases in line 15-of`Fig. 1 may themselves be at'suiciently'high temperatures, especially ifat least a portion of Athe-'gases is allowedV to byipass -heat exchanger4 =viailine14^duringthe start-up period.

Another still more efficient embodiment of the invention is illustratedin Fig. 2. Referring to Fig. 2, atmospheric air at about F.. may beintroduced into the system via line 201 which leads to low-pressurecompressor 202. In compressor 202 the air may be compressed and itstemperature raised thereby to around 300 to 350 F. This air may then bepassed via line 203 through intercooler 204 whereinv it may be cooled toabout er 100 F. byheat exchange with cooling water passing through line205. The cooled compressed air may then be passed to-highepressurecompressory 206 Where it is compressed to a pressure preferably inexcess of 90 p. s. i. gauge and its temperature raised to about 350 F.or more.

This hot compressed air may then be passed Via line consecutivelythrough heat exchangers 208 and 209 where it acquires heat from othergas streams later to be described. Thus the compressed gas may beheated-to at least 600 or 800 F. before introductionv into combustor210. ln combustor 210 the compressed air is used to burn fuel injectedthrough line 211. Again, a large excess of air is used as describedearlier in connection with Fig. l andthe resulting oxygen-containingcombustion gas may be at a temperature of about 1300 F. or higher if'theturbine metal permits. This hot compressed gas is then passed via line212 to high-pressure turbine v213 through' which it is expanded to anintermediate pressure, e. g. 10 to 50 p. s. i. gauge or such` otherpressure as may be desired for catalyst regeneration. The powergenerated in turbine 213 may be used' to drive 'high-pressure compressor206 by means of shaft 214 as well as a useful load such as electricpower generatorv 215. The shaft speed in this particular instance may bebetween about 8500 and 9000 R. P. M. From turbine 213`the amount ofpartially expanded gas required for catalyst regeneration is preferablywithdrawn via line 240 or from an analogous intermediate stage passedthrough cooler 241 before continuing into regenerator vessel 220 whereit is usedto burn coke-like deposits off spent catalyst particles in thesame manner as described earlier in connection with` regenerator 17 ofFig. 1. However, whereas the hot ue gas was used for steam generation inFig. l, in the presently illustrated preferred embodimentthe hot ilue.gas from regenerator 220k is'passed via line 221 through heat exchanger209 where it transfers heat'to the incoming compressed air, thuscontributing towards a further fuel saving in the operation of theprocess. Finally, the ue gas from exchanger 209 is exhausted to theatmosphere, or may still be passed through a waste heat boiler forrecovery of additional heat therefrom.

The amount of partially expanded gas not required for regeneration maybe passed fromhighpressurev turbine 213 to low-pressure turbine 217 vialine 216. In turbine 217 it' is further expanded preferably toatmospheric pressure, yielding additional power and high eiciency. Thepower thus produced in low-pressure turbine 217 may be used to drivelow-pressure compressor or any other load via shaft 218 which may have aspeed of about 7000 to 7500 R. P. M.

The atmospheric gas exhausted from turbine 217 may be passed at about800 to 900 F. via line 219 through heat exchanger 208 land nally ventedthrough line 250, or at least a portion lof it may be recycled tolow-pressure compressor 202 via line'2'51 and further cooler 252. Inexchanger 208 some of the heat contained in the exhaust gas may be usedto preheat the freshly compressed air in lineA 207.

On theother hand, if -no net power `output is con' templated in theVsystem, or at any rate if all the air passing through the turbines isrequired for catalyst regeneration, then lthe `exhaust pressure of thelow-pressure turbine Vis set at 15 -to 20 p. s. i. gauge or whateverpres-` 'sure 'may' vbe 'desired :in catalyst regenerator 220.r In such acase no gas is drawn off'atanyaintermediateH'turbine stage "sueltasline-F240.' Instead, Vall the'air exhausted at the desired pressure fromlow-pressure turbine 217 is passed through line 219 and heat exchanger208 into catalyst regenerator 220. The intermediate pressure betweenturbine stages may of course be higher here than in the alternativedesign wherein the terminal exhaust gas is at substantially atmosphericpressure. For instance, Where the exhaust from the low-pressure turbineis at about 15 p. s. i. gauge, the intermediate turbine pressure may bebetween about 35 and 70 p. s. i. gauge, depending on the pressure of thehigh-pressure stage and other factors well known in turbine design.Also, it will be understood that where the turbine exhaust is at ahigher temperature than the regeneration flue gas, the position of heatexchangers 208 and 209 may be reversed so that the compressed air feedis preheated first by the flue gas and then by the turbine exhaust.

Having described the general nature of the invention as well as severalspecific embodiments thereof, it will be understood that still otherembodiments and modifications are possible without departing from thescope hereof. For instance, it is entirely feasible to pass a portion ofthe compressed air from the compressor directly to the turbine,by-passing the combustor as shown at 230 in Fig. 2, instead of feedingall the air through the com buston Likewise, it may often beadvantageous to have a multiple-stage combustor instead of the singlestage shown, particularly Where complete fuel clean-up is important.

The invention is particularly pointed out and claimed as follows.

I claim:

In a process for regenerating spent solid catalyst containing acarbonaceous deposit thereon, the improvement which comprisescompressing atmospheric air in at least one compression stage to apressure of from about 60 to about pounds per square inch gauge, passinga stream of said compressed atmospheric air through at least oneindirect heat exchange zone as a heat exchange medium and producing afinal temperature in said air stream of from about 300 F. to about 800F., mixing said air with fuel in a combustion zone in an air/ fuel ratiowherein said air is present in an amount from about 3 to about 6 timesthe theoretical requirement for complete combustion of said fuel,thereby to produce a hot combustion product rich in oxygen and at atemperature of at least 1300 F., passing said hot combustion productthrough at least one gas turbine, expanding said product therein to apressure of from about 10 to about 25 pounds per square inch gauge,generating motive power through said turbine and utilizing at least aportion of said motive power initially to compress said atmospheric airprior to mixing with said fuel in said combustion zone, passing a streamof said expanded combustion product into indirect heat exchange relationthrough a heat exchange zone and thence, at a temperature of at least600 F., passing said combustion product rich in oxygen into aregeneration zone for said spent solid catalyst wherein the oxygenpresent in said combustion product supports combustion of carbonaceousdeposits on said solid catalyst as supplied to said zone.

References Cited in the le of this patent UNITED STATES PATENTS2,346,750 Guyer Apr. 18, 1944 2,405,922 Wyman Aug. 13, 1946 2,420,534Gohr et al. May 13, 1947 2,443,402 Schulze June 15, 1948 2,449,096Wheeler Sept. 14, 1948 2,605,610 Hermitte et al. Aug. 5, 1952 2,608,055Welsh Aug. 26, 1952

